(Reuters) — The U.S. government is investigating General Motors Co.'s auto financing arm over subprime auto loans it made and securitized since 2007, the company disclosed on Monday.

General Motors Financial Co. Inc. said it was served with a subpoena from the Department of Justice directing it to turn over documents related to underwriting criteria.

The subpoena, which the company said was in connection with an investigation into possible violations of the civil fraud law FIRREA, also asked for information on the representations GM made about the criteria when the loans were pooled into securities.

Financial services firms have paid billions of dollars to resolve investigations under FIRREA into questionable mortgages pooled into securities in the run-up to the financial crisis. The new subpoena could be one of the first public acknowledgements that investigators are also looking at the securitization of subprime auto loans.

FIRREA, the Financial Institutions Reform, Recovery and Enforcement Act, allows the Justice Department to sue over fraud affecting a federally insured financial institution.

GM Financial was known as AmeriCredit Corp. until the carmaker acquired it in October 2010. It issued $2.15 billion in securities backed by subprime auto loans in the first six months of 2014, making it the second-largest issuer of such securities for the period.

The disclosure of the subpoena accompanies increased regulatory scrutiny of subprime auto loans.

The Office of the Comptroller of the Currency, which regulates national banks, warned in a June report that “signs of risk in auto lending are beginning to emerge.”

Its assessment was based on lenders’ willingness to lengthen terms, chase borrowers with lower credit scores, and offer loans to buy cars that exceeded the value of the vehicle.

The disclosure also comes as the auto industry increasingly relies on subprime auto loans for growth.

New auto loans to borrowers with the lowest credit scores were up 51% in the first quarter compared with the same period in 2013, according to Experian Automotive.

Meanwhile, new auto loans to borrowers with the highest credit scores were down 7% over the same time frame.

Separately, regulators have brought some recent cases against auto lenders over allegations of discrimination.

In December, GM’s former financing arm, Ally Financial Inc., agreed to pay $98 million to resolve claims by the Justice Department and the U.S. Consumer Financial Protection Bureau that it charged minority borrowers higher interest rates than white borrowers.

A Justice Department spokeswoman had no immediate comment on the new GM subpoena. A spokesman for the consumer financial bureau declined to comment on whether the agency was examining potential fraud by auto lenders in the origination or securitization of subprime loans.